A ball screw apparatus is frequently used in a straight sliding portion of an industrial robot, and is mainly used for a purpose of giving a straight moving amount in accordance with a rotating amount of a motor to a movable body such as a table. Such a ball screw apparatus is generally constituted by a screw shaft having a spiral ball rolling groove formed on an outer peripheral surface, and a nut member meshed with the screw shaft through a multiplicity of balls and provided with an endless track on which the balls circulate, and is structured such that when the screw shaft is connected to the motor and is rotated, a multiplicity of balls interposed between the screw shaft and the nut member circulate within the endless track provided in the nut member, and the nut member lightly performs a straight movement in an axial direction of the screw shaft in order to this.
On the contrary, in this kind of ball screw apparatus, each of the balls circulating within the ball endless track is mutually brought into contact with the balls positioned in front of and at the rear of the ball, whereby there are disadvantages such that the ball is prevented from smoothly circulating and a contact noise between the balls is rasping at a high rotation of the screw shaft, and as a structure for solving the disadvantages, a ball screw apparatus disclosed in Japanese Unexamined Utility Model Publication No. 5-27408 is suggested.
In the ball screw apparatus disclosed in the publication, a band-like retainer having a flexibility is provided within a ball endless track of a nut member in such a manner as to be capable of circulating and moving, and a ball pocket for receiving a ball is arranged in such a band-like retainer at a predetermined interval. Accordingly, the balls are received in the ball endless track of the nut member in a state of being arranged in the band-like retainer at a predetermined interval, whereby in the ball screw apparatus, the balls circulating within the endless track are prevented from being mutually brought into contact with each other.
In this case, as a structure of forming the ball endless track in the nut member of the ball screw apparatus, as shown in Japanese Unexamined Utility Model Publication No. 5-27408 mentioned above, a structure in which a ball circulating pipe for jumping over some winds of ball rolling grooves in the screw shaft is provided and a ball endless track is constructed with including some winds of ball rolling grooves, and as shown in FIG. 11, a deflector 103 for scooping up a ball 102 from a ball rolling groove 101 in the screw shaft 100 is fitted to an inner peripheral surface of a nut member 104 and the ball 102 rolling on the ball rolling groove 101 of the screw shaft 100 is returned only for a wind of the ball rolling groove 101 through the deflector 103 have been known.
In the former structure using the ball circulating pipe, since the pipe is formed to have a length such as to jump over some winds of ball rolling grooves and is relatively gently curved, even when the band-like retainer mentioned above is assembled in the ball endless track and circulated, the band-like retainer can be smoothly inserted to the ball circulating pipe by curbing the band-like retainer after bending it within the pipe in a proper direction.
However, in the structure using the latter deflector, although the ball endless track is formed in a substantially circular ring shape corresponding to a wind of the ball rolling groove, the ball rolling in an inner portion of the deflector suddenly displaces in an axial direction of the screw shaft only for a lead of the ball rolling groove, so that in the case of assembling the band-like retainer of Japanese Unexamined Utility Model Publication No. 5-27408 formed in a band plate shape in the ball endless track as it is, the band-like retainer is forcibly curbed in the inner portion of the deflector. Accordingly, there is a risk that the band-like retainer can not smoothly circulate in the inner portion of the ball endless track.